Longitudinal members, such as spinal rods, are often used in the surgical treatment of spinal disorders such as degenerative disc disease, disc herniations, scoliosis or other curvature abnormalities, and fractures. Different types of surgical treatments are used. In some cases, spinal fusion is indicated to inhibit relative motion between vertebral bodies. In other cases, dynamic implants are used to preserve motion between vertebral bodies. For either type of surgical treatment, longitudinal members may be attached to the exterior of two or more vertebrae, whether it is at a posterior, anterior, or lateral side of the vertebrae. In other embodiments, longitudinal members are attached to the vertebrae without the use of dynamic implants or spinal fusion.
Longitudinal members may provide a stable, rigid column that encourages bones to fuse after spinal-fusion surgery. Further, the longitudinal members may redirect stresses over a wider area away from a damaged or defective region. Also, rigid longitudinal members may restore the spine to its proper alignment. In some cases, flexible longitudinal members may be appropriate. Flexible longitudinal members may provide other advantages, such as increasing loading on interbody constructs, decreasing stress transfer to adjacent vertebral elements while bone-graft healing takes place, and generally balancing strength with flexibility.
Conventionally, longitudinal members are secured to vertebral members using rigid clamping devices. These clamping devices may be multi-axial in the sense that they are adjustable prior to securing. However, once secured, the clamping devices are locked in place. A surgeon may wish to implant a flexible rod system and have more freedom to control pivot points or the nature of the pivoting motion. At present, a surgeon might only have a choice between rigid and flexible longitudinal members, which may not necessarily provide the desired degree of flexibility.